As the size of electromechanical, electro-optical, and electronic fluidic systems shrink to micrometer and nanometer scales, components within those systems necessarily shrink as well. Smaller components require more precise processing techniques to ensure optimal system performance. Operation of the fluidic systems is extremely sensitive to the fluid flow characteristics within the system and, in particular, at locations in the fluidic system where sensor measurements are conducted.
In particular, fluidic systems that use acoustic devices (e.g., flexural plate wave devices) are very sensitive to flow characteristics of the fluid flowing through the fluidic system. Typical acoustic devices include surface acoustic wave devices, flexural plate wave devices, lamb wave devices and cantilever devices. Signals output by acoustic devices are typically monitored to determine properties (e.g., density and viscosity) of the fluid or, for example, the amount and/or number of biomolecular targets in the fluid sample that have bound to a surface of the acoustic device.
Acoustic devices couple to fluids predominantly through acoustic interaction between the acoustic device and the fluid. Acoustic devices also couple to fluids through some viscous interaction between the acoustic device and the fluid, however, the coupling is predominantly acoustic coupling. Viscous interaction devices couple to fluids predominantly through viscous interaction between the devices and the fluid. Typical viscous interaction devices include quartz microbalance (QCM) devices, shear harmonic surface acoustic wave devices, and acoustic plate mode devices. The term “surface acoustic wave” refers to the manner in which energy is carried in the device structure rather than how the device couples to the fluid. Acoustic devices are devices where fluid interacts over a substantial area of a plane of the device. Acoustic devices respond with substantial out of plane motion that couples acoustically to fluid in proximity to the plane of the device (i.e., kinetic energy, potential energy and losses are carried substantially in the fluid). Viscous interaction devices respond primarily with in-plane motion that does not couple acoustically to fluid in proximity to a plane of the device.
Because acoustic devices interact with the fluid, they are particularly sensitive to irregularities or variations in the fluid flow characteristics. Inadequately designed fluidic systems have poor macroscopic performance and lead to loss of sensitivity, accuracy and/or repeatability. These issues can be particularly important in systems used to detect or measure biomolecular targets in fluid samples.
Hence there is a need for fluidic systems and sensor devices in which uniform, repeatable flows are produced in the fluidic system and, in particular, in sensing regions of the fluidic systems.